Metal-melting pot



T. VAN ALLER.

METAL MELTING POT.

APPLICATION FILED 050.4, 1919.

94 954 Patented 0013. 25, 1921.

Flgg. 3. WA TTJ DEE/i555 Inventor: 1 Tycho Van Al ler,

b5 m w His Attorney rrono van snare,

cor-crane,

lessees.

Application filed December T 0 s52 10 7mm it may concern:

Be it known that l, 'lrorro VAN Annex, a citizen of the United States, residing at Schenectady, in the county of Schenectady, State or" New York, have invented certain new and useful improvements in Metal- Melting Pots, of which the following is a specification.

My invention relates to electrically heated metal melting pots, and has for its object an improved type of pots in which the metal is automatically maintained at a constant fusing temperature the use of melting pots for melting metals, such as tin and the like, the oxidation of the metal is an important factor. W here the metal is kept in molten condition for long periods the oxidation of the metal and its effect upon the container is a serious matter. This is particularly true in case the temperature of the molten metal becomes too high. ln the case of tin, for instance, the amount of onid which forms on the surface and must be thrown away is an important item. Furthei'more, the oxid adheres to the vessel thereby reducing its capacity, and being non-conducting, prevents the transmission of heat. This incrustation is almost impossible to remove and in time the container becomes useless.

I have found that the amount of oxid can be very greatly reduced loy continuously maintaining the proper temperature or approximately so. Tin and soldering metal should he at'a temperature of from 350 tov 400 degrees C. to be in the best condition for use. At these temperatures the rate of oxidation is very slow. The ditficulty heretofore has been to maintain this temperature. ()rdinarily, if left for a time with heat applied, the temperature will rise to a point at which oxidation is very rapid. On the other hand the heat applied must be suiticient to bring the metal to the proper temperature in a reasonable time and to return the metal to working temperature when cold metal is introduced. Various means automatically regulating the temperature have been proposed with varying degrees of success. They all involve, however, expensive apparatus and are complicated and liable to get 'out of order. I have found that by using a heating element made of nickel, I obtain a very satisfactory automatic regula- Specification of Letters 1919. Sort place the heating Patented L55,

tron. hiclrel, as is well known, has two mperature coetlicient of res Moreover at the temperature of from flOO degrees G at which the molten me is in its best working condition, the nic does not oxidize. Furthermore, nickel is generally quite pure and, therefore, dependable, whereas a metal like iron is of a arying composition so that its characteristics cannot be depended upon. Nickel is very flexible and will not crack when subjected tb severe bending. 011s of the most important points in its favor for use in metal melting pots is that at the temperature employed in melt ng pots the nickel has its greatest variation in resistance per degree of temperature. In order to take advantage of this quality of the nickel, however, it is necessary that the heat lag should be very small, that is, the heat should be transferred ouickly from the h ating units to the molten metal. ll ith an arrangement of this sort h ating units can be run at a, higher current density, thereby bringing the metal to its proper temperature quickly because of the fact that its resistance is automatically varied so as to regulate the current. Furthermore, changes in voltage such as ordinarily occur do not have any material efiect.

Another feature oi my invention is that unit in good thermal relation with the pot, so that the heat gen erated in the heating element may at all times be quickly transmitted to the molen metal, and any drop in the temperature of the molten metal may quickly ailect the unit, thus decreasing its resistance and thereby automatically increasing the current input.

This automatic heat regulation also causes, in case device is not being used, the current drop to point where the heat input equalizies the natural radiation loss thereby preventing the device from overheati. -g and thus automatically prolonging the lite of the pot and its contents. The heating unit is designed so the heat input at working temperature equals the radi tion loss. Since the current duced automatically, only a sma amount of heat need be radiated, and creiore a small radiating surface will be suhlcient.

' Further objects of my invention will appear from the iollowi detailed description when taken in connection with the acco been re- Mill Qua

panying drawings in which Figure 1 is a perspective view of a metal melting pot with a part thereof broken away embodying my invention, Fig, 2 is a section taken on the line 2-42, of Fig. l, and Fig. 3 is a diagram of curves oi the temperature of the molten metal and the wattage,

Referring to the drawings, 1. is a recepta'cle for the material to be fused, which is made of any suitable material, 'lhis'receptacle is provided with a flange 2 at its open end, which flange serves as a means of support in a casing 23, The casing 3 is preferably made of sheet metal and is provided with tour legs at, 4: 4:3, i which support the complete unit. The outer surfaces of the receptacle 1 are in order that a heating unit may be placed in close thermal relation therewith. in the preferred form, this receptacle is provided with four rectangular sides and bottom as shown in the drawings, A; heating unit 5 is placed in close thermal relation. with each oi said sides and bottom, llhese heating units are made oi an element having a positive temperature coeficient, preferably nickel (i, which is wound around a fiat piece of insulating material 7, preferably mica, or any other way known to the art, and such a i is secured to each oi said sides and bottom. oi the pot by means of 'a metal clamp 8 and screw bolts 9 and 10 respectively. The 8 is made of a metal having the same temperature coefficient oi exaansion as the receptacle 1, and its object is to prevent the warping of heating unit 5, and hold it in close thermal relation with the receptacle it will be observed from Fig. 2 that the unit 5 is insn lated from the sides of the receptacle by a strip of i ica l1, other suitable material and from clamp 8 by a similar insulating member 12 The several units 5 are electrically connected in series to suitable termitrials intervening space between the receptacle i and the casing 3 is filled with a suitable heat insulating refractory material, such as asbestos wool 13.

v Having described the construction of a meltins" pot embodying my invention, its operation will be readily understood. When fusing metals, such as tin, soldering metal, and the like, it is desirable to quickly re duce the metal to a molten state and there after maintain it at some constant temperature, in the case of tin, solderins metals, and the like, at from 350 to 400 degrees (3. Unvionsly, when more cold metal is placed in the receptacle 1, the temperature will be lowered, in which case the watts input must be increased to fnse'the cold metal and then reduced to maintain the desired temperature of the molten metal: This regulation l accomplish automatically by using a heating eleinent, aving a positive temperature co eficient oi resistancew it is of course under necessastood that the resistance of such an element increases proportionately with increases in temperature, which correspondingly decreases the current. It is clear then that with a constant voltage, at some temperature the currentwill also be constant. As stated hereinbefore, in the case of tin, soldering metal and the like after reduced to the molten state the temperature should be maintained at from 350 to 400 degrees C. I have found that a heating element or" nickel produces the desired result. For example, as shown by the curve W in Fig. 3, with an input of 2400 watts at 115 volts, at the end of an hour the watts have dropped to 1200, while the metal has been raised to approximately 800 degrees C as shown by curve T. At the end of one and a half hours, the watts have dropped to 1100, while the metal has been raised to approximately 375 degrees C, which is the proper working temperature; Thereafter the wattage and temperature of the metal remain practically constant due to the increased resistance of the nickel element. A slig-t variation in voltage will not affect the operation described it is also obvious that to maintain the molten metal at a. constant temperature, the heat input must equal the radiation loss. As previously stated, this is taken care of hy so designing the unit so that the input equals the radiation loss at the working temperature While I have described my invention as embodied in concrete form and as operating in a specific manner in accordance with the provisions oi the patent statutes,. it should be understood. that I do not limit my invention thereto, since various modifications will suggest themselves to those skilled in the .art without departing from the spirit of my invention, the scope of which is set forth in the annexed claims.

What I claim as new and desire to secure Letters Patent of the United States is 1. An electrically heated melting" pot, comprising a receptacle for the material to belused and a heating unit in good thermal relation therewith, having such a positive temperature coefiicient of resistance that a constant working temperature is maintained regardless of the working condition within the pot.-

2. An electrically heated melting pot, comprising receptacle for the material to be fused and a heating unit in good thermal. relation therewith to rapidly raise said material to the working temperature, said unit having such a positive temperature coefiicient oi resistance that said working temperature will be constantly maintained.

3. electrically heated melting pot, compris ng a receptacle for the material to be fused and a heating unit in good thermal relation therewith, having such a positive temperature coeflicient of resistance that a constant working temperature is maintained regardless ofthe working condition within the pot, said heating unit being so designed that the heat input equals radiation losses at v the working temperature of the metal.

4. An electrically heated melting pot, comprising a receptacle for the material to be fused, a heating unit in good thermal relation therewith having a nickel resistance element so designed that the heat input equals the radiation losses .at the working temperature of the metal.

5. An electrically heated melting pot, comprising a receptacle for the material to be fused, a heating unit in good thermal relation therewith having a nickel resistance element whereby a constant working temperature is maintained regardless. of the working condition within the pot.

In witness whereof, I have hereunto set my hand this 2nd da of December, 1919.

T CHO VAN ALLER. 

